1. Field of the Invention
The present invention relates generally to the recycling of rubber products. More particularly, the present invention relates to methods and compositions wherein comminuted scrap rubber is incorporated into a polyurethane matrix to form a wide variety of useful materials and products.
2. Description of Related Art
The recycling of rubber products has received a great deal of attention in recent years. Typical rubber recycling processes involve grinding or otherwise comminuting scrap rubber product to form rubber particles. These rubber particles are recycled by mixing them with various different binders and molding or otherwise fabricating the rubber-binder mixture into desired articles. Typical uses for recycled rubber particles include the formation of various underlayments, surface coatings, tires, and other articles where a strong and resilient material is required. The binders which have been used to form the composites of recycled rubber particles include asphalt, synthetic and natural rubber, epoxies, and polyurethanes.
The majority of rubber recycling effort has been directed toward automobile and truck tires. The extremely large amount of automobile and truck tires which are discarded each year require that some degree of recycling occur. Processes used to recycle automobile and truck tires must necessarily be well suited for handling large quantities of recycled material. The process must be capable of taking large quantities of rubber particles directly from tire grinding and shredding equipment and transforming the particles into a useful material which can be molded or shaped into desired finished products.
Polyurethane is a popular binder which has been used to form composites with recycled rubber particles. A common procedure for forming polyurethane involves mixing a polyisocyanate with a polyol and suitable catalyst. The resulting polyurethane will be a non-cellular material provided that a blowing agent is not added to the composition. Water functions as a blowing agent during polyurethane formation because the carbon dioxide generated by the reaction of water and isocyanate becomes trapped within the polyurethane matrix and produces a foam structure.
There are many uses for polyurethane composite materials where the recycled rubber particles are incorporated into a polyurethane foam structure. However, there are also many situations where it would be desirable to have the recycled rubber particles present in a non-cellular or non-foam polyurethane matrix. Such non-cellular polyurethane composite materials are well suited for use in tires, shoe and boot soles, mattings, and other applications where a high degree strength and wear resistance is required.
There presently is a need to provide a process in which rubber tires and other discarded rubber products can be incorporated into a polyurethane matrix in a simple and efficient manner to provide a non-cellular polyurethane composite material which has adequate functional properties including high strength and wear resistance.